[The Horological Journal. Vol. ??, No. ?? (October, 1877): 21-23.]
The fascination which the re-winder principle has always had for inventors and students of horological escapements (as evidenced by the contrivances of Huyghens, Harrison, Mudge, Breguet, Cumming, amongst the old masters, and in recent years in the inventions of Professor Bloxam, Sir George Airy, Sir Edmund Beckett, and others) has lost none of its power. Hardly a year passes but that one or two constant force escapements (as the French call them) are added to the long list of patented inventions; and when one person goes as far as patenting, a dozen at least spend time and money on experiments in the same direction. [Page 22] It is proposed in a series of articles to illustrate the less well-known re-winder escapements, in the hope that experimenters, seeing what has been done, may not only be spared the waste of reproducing old ideas, but standing, as it were, on the shoulders of their predecessors, may discover, and benefit us with some real chronometrical improvement.
At one time, no doubt, the remontoire principle was expected to fulfil the part performed by the isochronism of the pendulum or balance spring. Now knowing that in that isochronism alone (combined with perfect compensation for temperature) lies the true time-keeping principle, the object of the new remontoires is, or should be, to give the pendulum or balance-spring the fairest possible chance, if the expression may be used, and to make the impulse1 (disturbance) a constant quantity.
Remontoires may be said to be divided into four classes:
First. - Those called train remontoires, in which the weight or spring wound up by the train drives the escape wheel. Harrison's re-winder, in his prize marine chronometer, was of this kind; see Aitkin's escapement, given2 with this article.
Second. - Those in which the pendulum or balance wheel does not find the "maintainer" wound up, but the train has to effect the re-winding, when the pendulum or balance unlocks it. The Astronomer-Royal's duplex spring escapement (see drawings) illustrates this method.
Third. - Those in which the re-winding is done when the pendulum or balance is out of the way, but the train has to be unlocked by the pendulum. C. G. Mudge's escapement, see HOROLOGICAL JOURNAL, Vol. II., page 17, and Mudge's own description.
Fourth. - Those in which the pendulum has only to unlock the maintainer, and the unlocking of the train is effected by the maintainer when the pendulum is out of connection with it; see Breguet and Garnier's escapement, given in last number.
The first class give, no doubt, a constant impulse, but all the escapement errors remain, and the clock must not be allowed to run down, otherwise the remontoire will run down also, and require some skilled person to put it right again.
In class two, this danger is done away with; but these remontoires are very dependent on the train, which it is essential must move quickly and promptly.
In three, the connection of the train with the pendulum is reduced to a minimum.
In four, the pendulum is entirely independent of the wheel work.
Description of Mr. John Aitkin's3 train remontoire, for which a prize of twenty guineas was awarded by the Society of Arts, 1824.
Fig. 1 is a front view, and Fig. 2 [a] side view of the escapement.
[Note: These figures were originally gathered into a full-page plate. In the original plate, Fig. 2 appears to the left of Fig. 1, and overlaps it slightly. The vertical assembly A-A in the illustration above is part of Fig. 2. Similarly, the two concentric circles in the lower right portion of the illustration below are actually part of Fig. 1.]
The same letters refer to the same part in each figure. The escape wheel G is actuated entirely by the helical spring t, the pinion g and collet s ride freely on the escape wheel, one end of the spring t is screwed to the collet u of the escape wheel, and the other end to the collet s on the socket of pinion g. [Note: collet s is only labelled in Fig. 3 below]
The third wheel of the train F gears into the pinion h, and also into pinion g, and so keeps the train locked by one of the eight long teeth, j, k, l, m, n, o, p, q resting on an enlarged part of the escape wheel arbor.
The teeth escape through the notches 1, 2, 3, 4, 5, 6, 7, 8 as the escape wheel turns around; fig. 4 shows positions of notches, as each escapes and allows wheel F to turn; that wheel being also in gear with pinion G, turns collet s around one-eighth of a turn, and so winds up helical spring t.
Fig. 3 is an enlarged view of the escape wheel axis. Fig. 4 shows the position of the gaps. Fig. 5 is an end view of collet s; fig. 6 [an] end view of collet u.
Figs. 3 and 4
Figs. 5 and 6
The Astronomer Royal's duplex spring escapement4 (figs. 7, 8, and 9).
[Sir George Biddell Airy (1801 - 1892) was Astronomer Royal of the UK from 1835 to 1881.]
The small escape-wheel is driven by the helical spring (seen in side view, fig. 8), and gives impulse on the pallets of the large anchor: the train is locked by the large escape-wheel on one or other pallet of the small anchor. The pendulum moving the anchor unlocks the train, the larger escape-wheel runs on and locks, winding up the helical spring. The small escape-wheel impelled by the spring lifts the pallet of its anchor, and thus gives impulse.
This is not the exact form of the original escapement, it is represented as drawn to show the principle clearly.
Figs. 7, 8, 9
1 To prolong artificially in any way the vibrations of a pendulum or spring is, in mathematical language, to disturb it.
2 From the Society of Arts' Transactions, 1824.
3 Aitkin lived at 55, St. John Street, Clerkenwell. This escapement is given only because it is historically interesting. For a really successful spring remontoire, see Sir Edmund Beckett's arrangement, sixth edition, page 218.
4 Denison's "Rudimentary Treatise;" Edition 1850, p. 67.
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